[R] "[[" gotcha
Petr Pikal
petr.pikal at precheza.cz
Tue Jan 16 11:43:03 CET 2007
Hi
try different way of list definition, see below.
On 16 Jan 2007 at 10:10, Robin Hankin wrote:
From: Robin Hankin <r.hankin at noc.soton.ac.uk>
Date sent: Tue, 16 Jan 2007 10:10:42 +0000
To: RHelp help <r-help at stat.math.ethz.ch>
Subject: [R] "[[" gotcha
> The following gotcha caught me off-guard just now.
>
> I have two matrices, a and b:
>
>
> a <- matrix(1,3,3)
> b <- matrix(1,1,1)
>
> (note that both "a" and "b" are matrices).
>
> I want them in a list:
>
B<-vector("list", 2)
B[[1]]<-a
B[[1]]<-b
here is no complain.
HTH
Petr
> > B <- NULL
> > B[[1]] <- a
> > B[[2]] <- b
> > B
> [[1]]
> [,1] [,2] [,3]
> [1,] 1 1 1
> [2,] 1 1 1
> [3,] 1 1 1
>
> [[2]]
> [,1]
> [1,] 1
>
> >
>
> This is fine.
>
> But swapping "a" and "b" over does not behave as desired:
>
>
> > B <- NULL
> > B[[1]] <- b
> > B[[2]] <- a
> Error in B[[2]] <- a : more elements supplied than there are to
> replace
> >
>
>
>
> The error is given because after B[[1]] <- a, the variable B is
> just a scalar and not a matrix (why is this?)
>
> What's the bulletproof method for assigning matrices to a list (whose
> length is not known at runtime)?
>
>
>
>
>
>
>
>
> --
> Robin Hankin
> Uncertainty Analyst
> National Oceanography Centre, Southampton
> European Way, Southampton SO14 3ZH, UK
> tel 023-8059-7743
>
> ______________________________________________
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html and provide commented,
> minimal, self-contained, reproducible code.
Petr Pikal
petr.pikal at precheza.cz
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